Ferromagnetic or ferrimagnetic (collectively "FM") oxide materials have found widespread use in passive circuit components, e.g., in resonators or inductors, because the low conductivity of these materials eliminates eddy current losses. Typically the materials are used in bull or thick film form, although their use in thin film form is not precluded.
In prior art devices it is typically not possible to ensure that the FM oxide material contains a single magnetic domain, since readily encountered stray fields of only a few oersted can destroy a pre-existing single-domain state, thereby introducing domain walls into the material. However, the presence of domain walls results in power dissipation in an applied time-varying field, limiting the usefulness of prior art FM oxide circuit elements typically to frequencies of about 10 MHz or less.
In view of the current rapid growth of the utilization of the frequency region of about 100 MHz-2 GHz for communication purposes (e.g., for cellular telephony), it would be highly desirable to have available circuit elements that comprise FM oxide material that can be single domain in substantially any stray magnetic field such a circuit element is likely to encounter, and that thus is not limited by dissipation due to domain wall motion. More specifically, it would be highly desirable to have available FM oxide-containing circuit elements that can be used at higher frequencies than prior art FM oxide elements, exemplarily including the range 100 MHz-2 GHz. This application discloses a technique for obtaining such elements, and elements produced thereby.
It is well known that the quantum mechanical exchange interaction can lead to spin coupling across the interface between two magnetically ordered materials. The resulting interface energy leads to exchange anisotropy. See, for instance, A. Yelon, "Physics of Thin Films", Academic Press, New York 1971, VoL 6, pp. 205-300.
Exchange anisotropy has been observed at room temperature only in a relatively small number of material combinations (typically thin films), which are, to the best of our knowledge, either metal/metal or metal/oxide combinations.
A particular metal/metal exchange coupled combination (MnFe/NiFe) has attained technological significance as the basis for a biasing scheme for magnetoresistive (MR) heads used in magnetic data storage. See, for instance, C. Tsang, IEEE Trans. Mag., Vol. 25, 3692 (1989). Note that MnFe is an antiferromagnet (AFM), and Ni.sub.1-x Fe.sub.x (PERMALLOY) is a soft FM material. M-H loop offsets in the range 10-100 Oe are obtained in this system, with blocking temperatures (above which the exchange anisotropy is negligible) of about 250.degree. C.
K. I. Arai et at., IEEE Trans. Mag., Vol. 27, 5337 (1991) report the application of YIG (yttrium iron garnet) to thin film inductors, with an external field applied to suppress domain-wall motion and consequent dissipation.
For a brief discussion of some aspects of exchange anisotropy, see B. D. Cullity, "Introduction to Magnetic Materials", Addison-Wesley 1972, pp. 422-425, incorporated herein by reference.